1. Field of the Invention
The present invention generally concerns the grinding of the peripheral edge of an ophthalmic lens, whether this is to trim, bevel or groove it.
2. Description of the Prior Art
As is known, in order to match an ophthalmic lens to the contour of the ring or surround of the spectacle frame in which it must be mounted, it has to be appropriately trimmed, that is to say it must have conferred on it a contour which is an image of that of this ring or surround.
As is also known, when the ring or surround comprises an annular groove, commonly referred to as a bezel, in order to retain the ophthalmic lens, it is necessary to form on the peripheral edge of the ophthalmic lens, after it is trimmed, a rib or bevel, generally triangular in transverse cross-section, appropriate to its engagement in said groove.
Likewise, it is necessary to form a groove in it when the ring or surround of the spectacle frame concerned comprises a projecting tang for retaining it and/or when a flexible filament or binding of some kind to fit round the lens is associated with the ring or surround.
More often than not the trimming and bevelling or grooving thus required are carried out on a grinding machine which is equipped to this end with at least one appropriate grinding tool at a grinding station.
On a grinding machine of this kind, the ophthalmic lens to be processed is held with its edge in contact with a grinding tool and it is rotated on itself about an axis parallel to the axis of the tool.
In practice, the grinding machines employed usually comprise, for this purpose, at the grinding station, a support, commonly referred to as a bascule, to which the ophthalmic lens to be processed may be attached and which, in order to apply the lens to the grinding tool concerned, is pivotally mounted on the frame of the assembly, to pivot about an axis parallel to the axis of said grinding tool.
In practice the support employed comprises two shafts between which the ophthalmic lens to be processed may be inserted, to hold and rotate it, and with one of which a template is constrained to rotate.
This template, which has the same contour as the ring or surround of the spectacle frame to be equipped, is provided so as to delimit during trimming the depth of penetration to be observed for the grinding tool used, and to this end it bears on a follower with which it remains in contact at all times during the bevelling or grooving which follows on from such trimming.
When not in use, the support is naturally moved away from the grinding tool or tools at the grinding station.
Thus after fitting an ophthalmic lens to a support of this kind, the support must be pivoted to lower the ophthalmic lens into contact with the grinding tool for carrying out the initial trimming.
Then, following the bevelling or grooving of the processed ophthalmic lens, the support must be raised before the ophthalmic lens is removed from it.
At present, these operations are more often than not carried out manually.
They therefore require a relatively experienced operator, both to initiate the processing of an ophthalmic lens and to terminate it, and the operator is mobilized for a relatively long and therefore expensive period each time.
In French patent application No. 80 09808 filed Apr. 30, 1980 and published under the number 2.481.635 it is proposed to raise the support carrying the processed ophthalmic lens on completion of its processing by means of the follower associated with the template, which to this end is made mobile in order to push back the template in contact with it and, through the intermediary of the latter, the support.
However, to raise the support sufficiently the travel of the follower must be relatively great, which significantly complicates the assembly.
In French Pat. No. 1.240.167 the carriage or support carrying the part or lens processed is raised by means of a counterweight which, movably mounted on a rod, is released at the end of a predetermined time under the control of a cam.
Apart from the fact that a counterweight of this kind is operative only on an "on or off" basis and only for raising the support, the initial lowering of the support needed to initiate the processing must still be done manually.
The same applies to U.S. Pat. No. 2,528,952 in which a counterweight movably mounted under the control of actuator means is provided only for appropriate adjustment of the contact pressure between the lens being processed and the corresponding grinding tool while the processing is being done.
A general object of the present invention is an arrangement enabling these disadvantages to be avoided and further conferring other advantages.